1. Field of the Invention
The present invention relates to a radiation measuring device (bolometer) and also relates to a radiation measuring system designed to use same and consisting of a radiation measuring device exposed to the radiation and a reference measuring device shielded against the radiation.
2. Description of the Prior Art
In the large plasma machines commonly used today, an essential part of the heating capacity deposited in the plasma is transported to the wall of the vacuum vessel by electromagnetic radiation and neutral particles. In order to be able to predict the energy balance of the plasma, it is necessary to measure the radiation power absolutely, resolved as to time and space, over the spectral range in question. The spectral range to be measured extends from the infrared range to the range of soft X-radiation in the 10 keV area.
For wide-band radiation measurement, radiation measuring devices known as bolometers are used. These are radiation detectors which are sensitive to a wide spectral range (infrared to soft X-radiation). They measure the incident radiation power integrally. The mode of operation of the bolometer is based on the absorption of the radiation to be measured and the resulting rise in heat of the bolometer detector. The bolometer signal is proportional to the temperature increase of the detector and the sensitivity depends on the temperature coefficient of the physical effect exploited for measuring the temperature increase.
The following different types of bolometers are used in plasma physics:
(1) the semiconductor bolometer (germanium layer); PA0 (2) the thermistor bolometer (nickel absorber with a thermistor insulated therefrom); PA0 (3) the gold or platinum resistors (freely suspended in a convolute or spiral shape); PA0 (4) the pyroelectric bolometer; PA0 (5) the IR bolometer; PA0 (6) the foil bolometer; and PA0 (7) the Thermopile PA0 (1) small dimensions of the detector and consequently PA0 (2) small electrical capacity; PA0 (3) predetermined time constant; PA0 (4) resistance to gamma and neutron radiation; PA0 (5) use detectors which are thermally independent of each other; PA0 (6) use detectors which are electrically independent of each other; PA0 (7) eliminate thermal and electrical interference; PA0 (8) electrical disruptive strength; and PA0 (9) must be able to be used in a high vacuum up to 300.degree. C.
The radiation power density emitted on the plasma and hitting the detector is of magnitude of a few m.sup.W /cm.sup.2. The use of foil bolometers is recommended to measure such small radiation power densities in environments, where strong interferences are present caused by neutrons, .gamma.-radiation and/or electromagnetic signals.
Foil bolometers consist basically of three functionally different elements:
(a) an electrically insulating carrier foil with high mechanical stability, on which
(b) a high-value resistor layer with low heat capacity consisting of thin and narrow strips is arranged in a convoluted shape. On the other side of the foil there is
(c) an absorber layer located precisely over the resistor layer. The absorber layer is in contact on all its edges with a dissipator.
The direct relationship between the time required for the heat to dissipate in the direction of the dissipator and the dimensions of the absorber leads to relatively large configurations of the bolometer detector with the conventional design of foil bolometers. However, detectors with large configurations have the following disadvantages:
(a) screen effects of the geometrical optics, caused by the dimensions of the detector surface with respect to the distance of the detector from the object to be measured and its dimensions;
(b) require relatively high electrical capacity which makes it impossible to use carrier frequency signal transmission;
(c) lack of sensitivity of the signal transmission to low-frequency pick-up. When high-frequency heating is used for the plasma experiment, high pick-up must be expected for the bolometer measurements; and
(d) when a large number of such measuring devices are used large rooms are necessary to accommodate the measuring devices even in the case of very average space resolution.